Vietnamese citizens line up outside the walls of the U.S. Consulate in downtown Ho Chi Minh City. / Thomas Maresca for USA TODAY

by Thomas Maresca, Special for USA TODAY

by Thomas Maresca, Special for USA TODAY

HO CHI MINH CITY, Vietnam - Early each morning, a line forms outside the walls of the U.S. Consulate in downtown Ho Chi Minh City. Vietnamese citizens like 24-year-old Nguyen Phuong wait patiently, rain or shine, to pay $160 for a visa interview and a chance to get to the United States.

Despite a struggling economy, the United States is still seen as a promised land for many in Vietnam. Phuong, who is hoping to study at the University of Alabama, has been rejected for a visa four times, but his parents insist he keep trying.

"The traditional thinking is that the U.S. is No. 1," he said.

That belief is prevalent in many countries, and it has given rise to bribery schemes that are difficult to detect because U.S. officials who decide on visas are rarely questioned about their decisions, say experts familiar with the process.

"The way that the State Department is wired makes it easy for these types of things to happen," said Peter Van Buren, an author and 24-year veteran of the Foreign Service.

In one of the latest examples of visa fraud, a former U.S. diplomatic officer in Vietnam was indicted in July in a scheme that netted millions of dollars by approving visa requests from foreigners looking to work or go to school in the United States.

Michael Sestak, 42, the former head of the consulate's non-immigrant visa section, is accused of taking bribes to approve almost 500 visas between February and September 2012. Four co-conspirators were also named in the federal indictment on 27 counts of conspiracy, bribery and visa fraud.

Sestak, a former police officer and naval intelligence officer from Albany, N.Y., was accused of "unprecedented greed" by the prosecution. Two of his accused partners, Hong Vo, 27, a University of Colorado graduate from Denver, and her Vietnamese cousin Truc Huynh, 29, were arrested in Denver. They are being held while awaiting trial in a Washington, D.C., court.

The indictment stated that the racket raked in $10 million and represented "one of the largest bribery schemes of which the United States is aware."

But while the size of the scheme is unusual, the nature of the crime is not. Incidents such as this have occurred at U.S. embassies from China to Canada to Qatar over the past several years.

In July, foreign service officer Edy Zohar Rodrigues Duran, 42, was removed his post at the U.S. Consulate in Guyana due to allegations of selling visas for cash and sex.

The alleged crimes illustrate the weaknesses in a system that insiders warn remains vulnerable to manipulation because it allows individuals to decide visa requests with little oversight from above.

A report to Congress by the Department of Homeland Security's inspector general found that a survey of such officials indicated they had little communication with superiors and some were subjected to "inappropriate pressure" to approve visa applications without delay.

The U.S. Citizenship and Immigration Services, which oversees visa administration under DHS, acknowledged that the "subjective feeling" of undue pressure by workers was "troubling," but that the IG findings may have been flawed because they relied on a confidential online survey.

Non-immigrant visas - temporary visas for business, travel or study - can be particularly susceptible to abuse. Foreigners apply for the visas at the U.S. Consulate in their country, and the process typically involves a brief interview with a consular official.

U.S law states that applicants for a non-immigrant visa are required to demonstrate a strong reason to return home once the visa expires "to the satisfaction of the consular officer."

What that means in practice is that the power to issue a visa to the United States - one of the most sought-after documents in many parts of the world - is left to a single officer.

"With non-immigrant visas, a consular officer has enormous discretion when to issue and when to refuse," Peter Van Buren, an author and 24-year veteran of the Foreign Service, said. "The law is purposely ambiguous."

Furthermore, once visas are granted, the decisions are rarely scrutinized, according to other former diplomats, meaning the process lacks safety controls to detect fraud.

"I probably adjudicated well over 10,000 visas and no one ever asked me, 'Why did you issue this visa?' " said Dave Seminara, a journalist who was a diplomat from 2002 to 2007. "I was never asked to justify issuances, yet you're asked to justify refusals on an almost daily basis."

In many developing countries, a diplomat faces an almost constant stream of requests for personal favors to sob stories to outright offers of bribes for a visa, experts say.

"There's a huge amount of temptation," said Seminara, who served in Macedonia, Trinidad and Hungary. "When you live in these countries you know how much people want visas. (Diplomats) aren't living with blinders in these countries. They know how much these visas are worth."

In Vietnam, Sestak and his partners were able to charge up to $70,000 for a visa, an enormous sum in a country with an average annual income of $1,500.

Court documents claim that Sestak's partners found buyers through website and personal networks. The scheme targeted people who typically would be denied a visa, such as those who had previously been refused, and sought buyers in the United States who were eager to bring their relatives over.

The USA has a Vietnamese population of over 1.5 million, almost all of whom are first- and second-generation Americans. Advocates for the Asian-American community say the current immigration law exacerbates the problem of visa fraud, making it more difficult for families to reunite in the United States.

"The fact that this type of fraud could occur at all really shows the lengths to which people are willing to go to gain entry to the U.S.," said Jacinta Ma, deputy director of Asian Americans Advancing Justice, a Washington D.C.-based advocacy group.

"We think that fixing the immigration system will help people get to the United States legally, because currently there is more incentive to thwart our immigration system when the system just seems unfair and broken."

In 2012, 86% of immigrant visas issued for Asian countries were family-based. Provisions in a recent Senate bill proposing an overhaul of immigration laws would eliminate sibling-based visas and limit eligibility for married children of U.S. citizens. More emphasis would be placed on skills that potential visa-holders offer the country.

But individual foreign service officers in consulates around the world remain the first line of defense. It is a role that former diplomat Seminara thinks they shouldn't be playing.

"I think the two functions are really incompatible. You don't want to be asking diplomats to also be enforcing laws. Law enforcement and diplomacy are two different things."

Others say greater oversight is needed to fix the problem. Van Buren says that self-policing goes against the institutional nature of the State Department.

"The State Department imagines itself to be an elite organization and so it has a hard time imagining that its American officers are cheats," he said.

It was, in fact, not an internal investigation that revealed the visa scheme in Vietnam, but a local Vietnamese whistle-blower.

Edward Alden, a senior fellow at the Council on Foreign Relations, suggested that the State Department take a closer look at its practices.

"The only plausible response, I think, is robust internal control and review mechanisms, as well as external, independent oversight," he said.

Alden said the visa screening system has improved since 9/11 and is more likely to identify and bar national security threats from receiving visas.

"While abuses are still possible, as in this case, the system is far more robust, particularly from a national security and terrorism perspective."